From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755376AbaHASTT (ORCPT ); Fri, 1 Aug 2014 14:19:19 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:44794 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751460AbaHASTS (ORCPT ); Fri, 1 Aug 2014 14:19:18 -0400 Date: Fri, 1 Aug 2014 11:19:05 -0700 From: "Paul E. McKenney" To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, bobby.prani@gmail.com Subject: Re: [PATCH v2 tip/core/rcu 01/10] rcu: Add call_rcu_tasks() Message-ID: <20140801181905.GH4784@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140731003914.GA3872@linux.vnet.ibm.com> <1406767182-4356-1-git-send-email-paulmck@linux.vnet.ibm.com> <20140801155310.GA2945@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140801155310.GA2945@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14080118-1542-0000-0000-000003B326FA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 01, 2014 at 05:53:10PM +0200, Oleg Nesterov wrote: > On 07/30, Paul E. McKenney wrote: > > > > + rcu_read_lock(); > > + for_each_process_thread(g, t) { > > + if (t != current && ACCESS_ONCE(t->on_rq) && > > + !is_idle_task(t)) { > > + t->rcu_tasks_nvcsw = ACCESS_ONCE(t->nvcsw); > > + t->rcu_tasks_holdout = 1; > > + list_add(&t->rcu_tasks_holdout_list, > > + &rcu_tasks_holdouts); > > + } > > + } > > + rcu_read_unlock(); > > Wait, unless I missed something this can't work... > > The problem is, once the exiting task passes exit_notify() it can > be removed from rcu lists. > > Now suppose that (say) proc_exit_connector() has a probe, and this > task has jumped into trampoline and it was preempted there. > > No? OK, this sounds to me like another vote for get_task_struct() as used in the v3 series. Or am I missing something? Thanx, Paul